i tried and was unsuccessful. i was told if the car is recent in production and you are getting an aftermarket ALPINE deck (since alot of bmw cd changers are by alpine), they should find a way to do it.

The stock head units (at least in my car, maybe I'm imagining it. I don't think so though) have a feature that raises the volume as the car gains speed. It kicks in around 40, or so. It's a feature I had on an ACDelco HU in my Cavalier. Ended up blowing my speakers because of it (It tries to get REALLY loud when your doing 80). I may just pull the HU and see what I can finger out.